| 摘要 |
PURPOSE:To obtain a high tension invert having good weldability and tougheness by subjecting a steel consisting of a prescribed component compsn. and having the C equiv. expressed by the specific formula to hot rolling at respectively controlled cumulative rolling reduction and finish temp. CONSTITUTION:The steel contg., by weight, 0.05-0.16% C, 0.05-0.35% Si, 1.0-1.50% Mn, <=0.020% P, <=0.0105 S, 0.010-0.060% sol.Al, and <=0.0050% N and having the C equiv. expressed by the formula satisfying 0.28-9.35% is hot rolled in the following manner: Said steel is subjected to the hot rolling at 2T (T is the wall thickness of the product) cumulative rolling reduction at <=900 deg.C and the temp. difference in the respective parts of the material to be welded in said stage kept within 20 deg.C by means such as water cooling and at 720-650 deg.C finish temp. As a result, the invert which is provided with the substantial strength and toughness in spite of the low carbon equiv. steel having the good weldability and has the extremely less strength difference between the web and flanges as compared to the product formed by ordinary controlled rolling is stably produced with high efficiency.
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